Abstract: The performance of the yield surfaces of saturated sand is presented in this paper. The objective of this study is to improve the shear yield criterion and volumetric yield criterion in the constitutive model of sand material. A new type of nonlinear shear yield criterion and an improved volumetric yield criterion are proposed. The new shear yield criterion adopts a quadratic polynomial to describe the shear yield surface. The improved volumetric yield criterion combines ellipse, linear and smooth functions to describe the volumetric yield surface. These criteria are verified by the triaxial compression test data of Ottawa sand and Earls Creek sand. The research shows that the nonlinear shear yield criterion can describe the nonlinear growth of the shear yield surface on the q-p plane with the increase of the effective mean stress, as well as the phenomenon that the shear yield surface does not pass through the origin of the q-p plane. The improved volumetric yield criterion can describe the phenomena that the contractive and dilatant parts of the volumetric yield surface on the q-p plane move and deform in the positive direction of the p axis with the increase of the confining pressure, and that the volumetric yield surface is smooth everywhere. The results indicate that the new criteria can accurately describe the yield characteristics of sands and are of great significance for promoting the theoretical development of the soil constitutive model.

Key words: Rock and Soil Mechanics, Nonlinear Properties, Smooth, Shear, Volume, Yield Criteria